During the operation of an internal combustion engine, exhaust gases arise, which contain various pollutants. In diesel engines the main components of these pollutants are, for example, soot and nitric oxides (NOx). In order to comply with legal regulations with regard to admissible emissions of pollutants, the attempt is made on the one hand to already reduce the untreated emissions arising during combustion by means of engine modifications and on the other hand to achieve a second reduction of the pollutants contained in the exhaust gas by means of modifications outside of the engine. Diesel particle filters, NOx storage catalytic converters or SCR catalytic converters are employed, for example, as modifications outside of the engine. Besides an appropriate choice of the air/fuel mixture, an exhaust gas recirculation serves as an example of an engine modification.
In order to maintain an effective reduction of the soot and NOx emissions, it is necessary to ascertain a value, which describes the pollutant emission currently produced, already during the operation of the internal combustion engine. In so doing, the current soot and NOx emissions can, for example, already be ascertained during the operation of the internal combustion engine. Such items of information can then be used to detect the depletion of a diesel particle filter, respectively a NOx storage catalytic converter, and if need be control a regeneration of the diesel particle filter, respectively the NOx storage catalytic converter, in an open-loop, respectively closed-loop.
The emissions of pollutants of an internal combustion engine are dependent on regional parameters in the combustion chamber, as, for example, the regional air/fuel ratio or the maximum combustion temperature. These parameters can, however, only be measured using a special measurement and test engineering, as, for example, a rapid gas extraction valve or a so-called multi-spectral pyrometry. Such engineering is, however, not presently available in internal combustion engines and will not be available in the future in series production engines.
The arrangement of a measuring probe for the acquisition of a combustion radiation in an internal combustion engine is known from the German patent DE 103 30 819 A1. A combustion radiation emitted in the combustion of the internal combustion engine during the combustion of the air/fuel mixture is acquired by said probe, the combustion radiation being composed of various components, for example a soot radiation and an OH radiation. The radiation intensity is ascertained from a certain segment of the progression spectrum of the combustion radiation in the known method, the intensities of the soot radiation being ascertained in the range of 500 to 8000 nm, of the aldehyde bands at 375 to 385 nm and at 425 to 435 nm and of the OH radiation at 305 to 315 nm. For this purpose, the combustion radiation acquired by the measuring probe is supplied to a soot detector, an OH radiation detector and to a plurality of aldehyde detectors, which operate in certain wave ranges, for ascertaining the radiation intensity of the certain wave range. The intensities are additionally supplied to an evaluation unit, which ascertains if a homogeneous combustion prevails.
A test is made using the soot detector in the known method to determine whether a specified threshold value, which characterizes a homogeneous combustion, has been exceeded. If the threshold value has been exceeded, the mixture formation is accordingly manipulated by means of a control unit. Besides high costs for the required sensor system, the functional vulnerability of the sensors when exposed to contaminants and coating by soot is a disadvantage to this method. Moreover, in order to implement the method, application is complex.
Particularly the cylinder pressure initiated by the crankshaft angle, respectively the characteristic values derived from said pressure and their progressions, is basically suited for determining the soot and NOx emissions with the standard measurement instrumentation available in the motor vehicle. This can be attributed to the fact that the progression of the cylinder pressure is a state variable of the combustion. Said variable is essentially independent of region and describes the energy conversion in the cylinder of an internal combustion engine and consequently has a close correlation with the combustion.
A method for determining the soot concentration in self-igniting internal combustion engines using a neural network is known from the German patent DE 197 41 973 C1. In this regard the neural network is initially trained using learning data specifically intended for this purpose. This learning data is the input data representing the soot concentration. The input data comprises in particular variables characterizing the cylinder pressure, which, for example, consist of the maximum value of the cylinder pressure, the integral of the cylinder pressure versus a certain crankshaft angle or something similar. The temporal progression of the cylinder pressure, the combustion curve, the temperature curve and/or the burn-through function curve can however also be used as input data, said data being ascertained using a combustion curve calculation. Particularly the geometry of the piston and the combustion chamber, the engine rotational speed, the fuel/air ratio, residual gas and the initiation of combustion can also be used as additional input data.
After training the neural network, a neural network is available, which allows for a mapping of the selected items of input information to the soot concentration, wherein the correlations between the input variables and the soot concentration are contained and can accordingly be extracted. In so doing, the relevant characteristics of the input data are identified and there relevance can be appraised. The disadvantage with this is that only a few characteristics, which characterize the progression of the combustion, can be derived from the cylinder pressure progression in the known method.
The depositing of datasets into engine characteristic maps in a control unit, which controls the operation of the internal combustion engine in an open or closed loop, is also known from the German patent DE 197 41 973 C1. Items of information concerning the correlations between the input data and the measured values of the output variable, the soot concentration, are thereby described. These datasets are, for example, ascertained by means of complicated measurements in the internal combustion engine or from the combustion curve calculations.
It is the task of the invention to propose a possibility for determining the soot and NOx emissions, whereby the emissions can be ascertained using standard measurement and test engineering, a high degree of accuracy in the ascertainment being simultaneously achieved.